Using the design of experiments methodology to evaluate the heat treatment of additively manufactured maraging steel

Abstract

The effect of the processing parameters on the final microstructure and mechanical properties was investigated for additively manufactured maraging tool steel 1.2709. First, an effective range of appropriate combinations of heat treatment parameters was found using the design of experiments (DOE) method. This suggested 17 variations of heat treatment regimes. The effect of input parameters (initial condition, hardening temperature, hold at hardening temperature) on the output values (mechanical properties) was then statistically evaluated. Three initial conditions of the additively manufactured (AM) steel were used: as-built, annealed at 820 °C for 1 h and annealed at 940 °C for 2 h. A subsequent heat treatment in the region of 250 °C–750 °C was considered with holds of 0–6 h at the temperatures. Based on the measured mechanical properties, regression analysis was performed and optimal models for the prediction of individual mechanical properties were produced. The coefficient of determination of the models for yield and ultimate strengths and hardness reached above 95% when hardening temperature was considered a significant factor. It was around 98% in the case of tensile strength and hardness when the additional effect of the initial condition was also included in the models. This means a very reliable prediction of those mechanical properties can be expected. On the other hand, the model for total elongation can explain only 41% of the measured values, as not a single statistically significant factor was identified.

Keywords

• Maraging steel
• Additive manufacturing
• Powder bed fusion
• Precipitation hardening
• Heat treatment
• Design of experiment